The missiles were fired as the vehicle carrying the militants was passing by a house in Paikhel area of Datta Khel sub-division, 28 miles (45 kilometers) southwest of Miranshah, the main town of North Waziristan Agency.

The house was extensively damaged in the attack. Exact identities of the dead militants were not known, though an intelligence official reportedly said that those killed were associated with the Haqqani network.

The Haqqani network is being run by Sirajuddin, son of Afghan warlord Jalaluddin Haqqani, and is linked to al-Qaeda and the Taliban.

The American military does not either confirm or deny drone attacks though it is widely known that only the U.S. is capable of deploying such hi-tech aircraft in the region.

U.S. Special Envoy for Pakistan and Afghanistan Richard Holbrooke on Friday had justified drone attacks on Federally Administered Tribal Areas (FATA) in Pakistan, stressing that some elements present in the western part of the nation posed a threat to several countries, and that a joint strategy was needed against them.

The Obama administration has stepped up drone attacks in Waziristan since the December 30 suicide-attack on a CIA forward operating base in the neighboring Khost province of Afghanistan that killed seven of the agency's operatives.

This month alone, the U.S. has carried out 13 drone strikes, killing over 70 militants in the Waziristan region described by Washington as the global headquarters of al-Qaeda and a stronghold of Haqqani network.

Islamabad officially objects to these drone strikes, saying they are violating its sovereignty and that they are stoking anti-American public wrath, as also bolstering support for militants, but is privately reconciled to it.